One type of telecommunication or digital storage systems is a reverse concatenation system. In one example of a reverse concatenation system, a transmitter or write processor includes a modulation encoder, an error correction encoder (or, more generally, a systematic encoder), and a parity encoder. A corresponding receiver or read processor includes a parity decoder, an error correction decoder (or, more generally, a systematic decoder), and a modulation decoder. It would be desirable to develop new systems and techniques that improve the performance of reverse concatenation and other systems.